The optimum amplification of a hearing aid for compensating loss of hearing is conventionally determined by loudness scalings or hearing threshold-based, prescriptive adaptation formulae. These formulae describe the target amplification as a function of the frequency and the sound level. The established formulae, such as NAL-NL1 or DSL-I/O, are defined for the frequency range 0 to 8 kHz. They say nothing about target amplification in the range above 8 kHz. This is primarily due to the fact that established hearing aids can only transmit frequencies below 8 kHz. An adaptation formula for high frequencies is therefore not required. In addition there is the fact that to measure high-pitch loss of hearing special audiometers are required and implementation of a defined amplification is very difficult in this frequency range (wavelength of the same order of magnitude as auricular canal geometries). However, as a result of special broadband amplifiers and electroacoustic converters hearing aids can nowadays be produced which can transmit frequencies above 8 kHz through to 15 kHz. One problem is accordingly adjustment of amplification in this frequency range to the loss of hearing, and this constitutes the subject matter of the present invention. In addition there is the fact that acoustic feedback can significantly affect the amplification adjustment. This applies to the entire frequency range in general but in particular to the frequency range above 6 kHz.
One approach to the solution to this problem lies in a loudness-normalizing adjustment. In this case amplification across the entire frequency range is adjusted by loudness scalings (narrow band stimuli) and comparison with reference scaling in people with normal hearing in such a way that the loudness impression normalizes, i.e. a stimulus with the hearing aid is perceived to be just as loud by a person who is hard of hearing as by a subject with normal hearing and without a hearing aid. Drawbacks in this connection are however the very long measuring times for the loudness scalings and the relatively frequent acoustic feedback. In addition, for the base frequency range it has not previously been possible to provide evidence of any advantage of a loudness-based adjustment over the “rapid”, prescriptive adaptation formulae requiring only measurement of the audiogram.
A method for adjusting a hearing aid is known from publication DE 699 16 756 T2 with which the object of compensating a patient's audiogram is achieved. This is achieved in that certain frequency bands are amplified or attenuated.
A hearing aid is also known from publication DE 690 12 582 T2 in which acoustic feedback is rendered ineffective.
Publication DE 44 41 755 C1 describes a hearing aid circuit in which a first frequency channel and a second frequency channel exist in one embodiment.
Publication DE 41 25 378 C1 also discloses a hearing aid with a signal path for a lower frequency range and a further signal path for an upper frequency range.
A method for adjusting a hearing aid is known from publication DE 35 42 566 A1. In this case the user can change the steepness of the frequency response above a limit frequency.
A method for recording information in a hearing aid is also known from publication EP 1 414 271 A2. The information can be used to adjust the volume and to avoid feedback.
Publication EP 0 917 397 A1 also discloses a method for determining a set of parameters for a hearing aid. In this case the volume and feedback are again taken into account.
Finally a method for measuring the individual acoustic ratios in a human ear in which an audiogram is created is described in publication CH 678 692 A5.